A liquid chromatograph is composed of a plurality of units, such as a pump, a liquid injector and a column oven. The operation of each unit is controlled according to control signals fed from a control system.
In recent years, in such a liquid chromatograph, a control system consisting of a computer having a predetermined controlling and processing program installed have been widely used in order to comprehensively control each analysis unit and process collected data. In such a control system, a continuous analysis of a number of samples or similar operation can be automatically performed by using a schedule table prepared in advance of the analysis (for example, see Patent Literature 1).
FIG. 7 shows one example of the schedule table used in a liquid chromatographic analysis. Each row of the table corresponds to one analysis and holds information necessary for performing the analysis, such as the sample number, the amount of sample to be injected, the name of a method file, and the name of a data file in which an analysis result is to be saved. The “method file” is a file in which the values of the parameters that specify operational conditions of each unit in the liquid chromatograph are stored. For example, this file contains analysis parameters which indicate the kinds or values of various configuration items, such as the kind of mobile phase and the kind of column to be used in the analysis, the flow rate of a pump and the temperature of the column oven during the analysis. (A set of analysis parameters used in one analysis is collectively called the “analysis method.”)
After the schedule table is prepared, when an order to initiate the analysis is given, an analysis of a number of samples is automatically performed, in which each sample is sequentially selected according to the schedule and the analysis conditions are set according to the analysis method specified in the corresponding method file.
In such a liquid chromatograph, a different analysis method yields a different result. FIGS. 8A and 8B illustrate how the result of an analysis changes when different analysis methods are used. FIGS. 8A and 8B each shows a chromatogram obtained by an analysis of the same sample using a gradient liquid-supply method (such an analysis is hereinafter called the “gradient analysis”) in which the proportion of solvent B in the mixed liquid was initially maintained at 90% for five minutes from the injection of the sample and subsequently lowered to 5% over two minutes. In FIG. 8A, solvent A is a 10-mmol/L solution of sodium citrate (pH 3.1) and solvent B is methanol. In FIG. 8B, solvent A is a 10-mmol/L solution of sodium acetate (pH 4.7) and solvent B is a 50:50 mixture of methanol and acetonitrile.
Since the result of an analysis thus changes depending on the analysis method, users need to perform a preliminary analysis for one sample under various conditions and select the most suitable analysis method for the sample based on the obtained results. Such a preliminary process (search) is called the “method scouting.”
In the method scouting, the user specifically sets the analysis parameters representing various configuration items, such as the kind of mobile phase, the kind of column, the value of the flow rate of the pump during the analysis, the value of the temperature of the column oven, the value of the composition ratio of the mobile phase (when it is composed of two solvents), and the range over which the composition ratio is changed with time (when a gradient analysis is performed). Subsequently, a number of method files each of which contains a different combination of the values of the analysis parameters within the specified ranges are exhaustively created by the user or the program, and a schedule table including those method files is created. Upon receiving an order to initiate the analysis, the system sequentially performs a plurality of analyses according to the conditions specified in each row of the schedule table. The chromatogram data obtained as a result of each analysis are compiled into one data file and saved in a storage device, such as a hard disk drive. Later on, the user browses through the chromatogram data saved in the storage device and selects, as the analysis method to be used in an actual analysis of the sample, an analysis condition under which the best analysis result has been obtained.